The present invention relates to the field of polymer blends, particularly to blends of a polyacetal and a polypropylene wherein compatibilizing agents are used.
Polyacetals are polymers having repeating units of the formula (--O--(CR.sub.1 R.sub.2).sub.n --) where R.sub.1 and R.sub.2 are independently either hydrogen or a lower alkyl group and n is an integer. The simplest polyacetal is polyoxymethylene, which has repeat units of the formula (--O--CH.sub.2 --). However, polyoxymethylene tends to decompose readily to form formaldehyde. One solution to this decomposition problem is to incorporate into this polymer a small percentage of units of higher polyoxyalkylenes, e.g., polyoxyethylene. Hoechst Celanese Corporation sells a polymer called CELCON.RTM. comprising about 98% oxymethylene units and about 2% oxyethylene units. CELCON.RTM. is usually made by copolymerizing trioxane (98%) and ethylene oxide (2%).
Another solution to the decomposition of polyoxymethylene is to put other units, e.g. acetate groups, on each end of the polymer. E. I. duPont de Nemours Co., Inc. sells such a polymer under the name Delrin.RTM..
Polypropylene comprises repeating units of (--CH(CH.sub.3)CH.sub.2 --). Polypropylene is relatively inert to chemical attack, but tends to be soft and is not stable at high temperature. Polyacetals, however, are more rigid and more stable at high temperatures but more vulnerable to chemical attack. A blend or a laminate combining these two types of polymers and having the best features of both would be very desirable. Unfortunately, these polymer do not adhere or blend well and tend to separate.
Polypropylene may be modified by grafting. For example, functional monomers such as acrylic acid or muconic acid (2,4-hexadienedioic acid) may be added to the polymer to form a modified polyolefin having a small percentage of functional groups attached to the main chain. Such modification may affect the compatibility or solubility of the polymer with certain other polymers or solvents.
Acrylic acid grafted polypropylene is available from BP chemicals. Cis,cis- and cis,trans-muconic acid are presently available from Celgene Corporation. Muconic acid grafted polypropylene is within the subject matter of a patent application filed on the same day as this application by the same inventors entitled, "MUCONIC ACID GRAFTED POLYOLEFIN COMPATIBILIZERS", the description of which is herein incorporated by reference.
Modified polyacetals may also be made. For example, a hydroxylated polyacetal may be produced by copolymerization and hydrolysis. A hydroxylated form of Celcon.RTM. may be produced by reacting trioxane with an ester co-monomer, such as a glycerol formal benzoate, and hydrolyzing the ester group. The resulting polymer contains units having pendant hydroxyl groups, e.g. (--CH.sub.2 --CH(OH)--) or (--CH(CH.sub.2 OH)--), interspersed between (--O--CH.sub.2 --) units. Further information regarding hydroxylated polyacetals may be found in co-pending U.S. patent applications Ser. Nos. 350,781, 350,782 and 350,791, the disclosures of which are herein incorporated by reference.
U.S. Pat. Nos. 4,455,273 and 4,584,347 describe modified polyolefin fibers wherein polyolefin graft copolymers and polyoxymethylenes may be used as additives.
U.S. Pat. No. 4,670,508 describes a thermoplastic resin composition comprising a thermoplastic resin, e.g. a polyacetal, and an ultrahigh molecular weight polyolefin.
U.S. Pat. No. 4,766,168 teaches a stabilized polyacetal composition wherein certain hydroxy containing polymers and/or oligomers may be added to a polyacetal molding composition.
U.S. Pat. No. 4,873,282 discloses a polyacetal resin composition containing a polyolefin and carbon black.
U.S. Pat. No. 4,556,690 describes an acetal resin composition that includes an modified alpha-olefin that is a graft polymerization product of an alpha-olefin and an unsaturated carboxylic acid or derivative thereof.
U.S. Pat. Nos. 4,214,034, 4,220,736, 4,250,661, and 4,266,370 are directed to agricultural covering films and sheets for thermal insulation comprising an acetal resin and a thermoplastic olefinic resin.
U.S. Pat. No. 4,816,530 disclose a polymer blend of a carbon monoxide-olefin copolymer and a polyacetal.
European Patent Application No. 89105785.3 filed Apr. 3, 1989 and having a publication no. 0 338 303 describes a thermoplastic resin composition comprising a polyoxymethylene resin and a multi-phase thermoplastic resin that includes an epoxy group-containing olefin copolymer.